Diseases of Farmyard PoultryPart 3 - Control of Coccidiosis

Disease background

Coccidiosis is one of the
most important poultry diseases worldwide and is ubiquitous, the
only limit to the distribution of this disease is the distribution
of the hosts.

Cause and clinical signs

A protozoal parasite which
multiplies in the gut, specific to different hosts. Not all species
of coccidia are harmful but there are five of the Eimeria
species pathogenic to chickens, five in turkeys, three in geese,
three in ducks and three in pheasants.

Enteritis (inflammation of
the intestine) is present in all coccidia infections and usually
accompanied by diarrhoea which may or may not have blood in it.
Poor growth and impaired feed conversion is common and mortality
can be increased.

Fig 1: Typical stance of a chick with
coccidiosis

Transmission

Parasitic phase: the
infective oocyst (coccidia egg) is eaten by the bird and then
multiplies over about 7 days within the gut, thousands of new
oocysts resulting from just one ingested oocyst.

Non-parasitic phase: excreted
in the droppings, the oocysts then take 2 days to mature (ideal
conditions 25-30ºC and moist) before being ready for the next host
to eat.

There are three types of
coccidia in chickens and this is reflected in the other
species:

Dayold chicks do not get immunity from their mother. Birds of
any age are susceptible, but most acquire infection early in life
which gives them some immunity. Immunity is best kept strong
by a low level of infection, which is what happens on free-range.
Birds kept or reared on litter are more at risk when the coccidia
has conditions which suit it such as wet litter. If the birds are
also stressed by environmental factors (cold, overcrowding, poor
ventilation) then disease results. The oocysts are very resistant
to destruction, either by disinfectants or by drying out and can
survive for months or years.

The species of coccidia have different areas of the gut which
they prefer, some producing the expected bloody diarrhoea, some
producing high levels of mucus, sometimes white diarrhoea, and
others stunting growth. Infection can show from 3-6 weeks of age
and infective oocysts can be transported by people looking after
the birds. Older birds can become infected if either their immunity
has been reduced due to being kept on a wire floor (no access to
droppings and therefore no trickle infection) and then put onto
litter, or if environmental stressors reduce their immunity. The
birds generally look hunched and depressed with or without blood in
the droppings.

Economic Impact

This disease is very common and unless
controlled has a severe economic impact. Even low levels of
infection cause ill thrift and loss of production with increased
mortality.

Diagnosis

Clinical signs plus a faecal sample containing oocysts and/or
post mortem where the intestines are dark purple and the
laboratory finds stages of the coccidia in the lining of them.

Fig 2: Oocysts in a faecal
sample

Fig 3: Intestines with necrotic
caeca

Treatment

Anticoccidial drugs in the feed for only the first 6 weeks of
life which reduce but not eliminate the numbers of coccidia has
been the norm in order to let the chicks have a low level of
infection and therefore acquire immunity. Permitted drugs in feed
are, however, being reduced on an annual basis across the
board. Resistance to the anticoccidial drugs has occured.

Free-range reduces the incidence of disease while still
providing trickle infection to boost immunity.

The only product currently licensed for treatment of a
coccidiosis outbreak in chickens is Baycox: this use is restricted
to broiler breeders on the data sheet (licence details).
Sulphonamides can be ordered from specialist poultry veterinary
practices. On a small scale and where the birds do not enter the
food chain, the pigeon product, Coxoid, is used by fanciers and
small-scale keepers. This contains amprolium which used to be
licensed for chickens and has proved to be safe.

There are no products licensed for treatment in turkeys and
waterfowl but Coxoid has been used with success. The coccidia life
cycle is similar to chickens and the oocysts persist in the ground
for months or years. Certain compounds are toxic and lethal to
turkeys, particularly the ionophores such as monensin, lasalocid,
salinomicin, narasin and maduramicin, therefore the label on the
feed bag must be checked to avoid these.

Temperatures above 56ºC and below freezing are lethal to
oocysts, as is desiccation. Oocysts can stay in sheds despite
disinfection unless a specific oocidal ("egg-killing") disinfectant
is used.

Vaccination

By far the better treatment and prevention for chickens is the
vaccine, Paracox. This contains all seven species of coccidia but
these are weakened so that they cause the chicken to mount an
immune response but not to become infected. As this is an
industrial product it normally comes in quantities to treat
thousands of birds. Paracox is available from PHS Pharmacy (01845
577907) with a prescription, in 100 and 200 dose containers.
Paracox will be administered once as a solution from a dropper
bottle to a healthy dayold chick via its mouth. The shelf-life of
the product will be 4 weeks, so orders need to be made with the
monthly expected hatch in mind. Any feed used for vaccinated birds
should not contain anticoccidial drugs as
this will counteract the vaccine. The vaccine can be used on
unvaccinated chicks up to 9 days old but is most effective at
dayold.

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